The prior art hydroentangling method involves the process to subject a card web to high pressure fluid jet streams in order to entangle fibers in web and thereby providing specific entangled structure and suitable mechanical properties to the web.
The nonwoven fabrics produced by this hydroentangling process permits higher mobility of fibers within the fabrics than any other textile fabrics and nonwoven fabrics because the fibers are simply mechanically entangled and not firmly bonded together. Therefore, they have soft and lint-free properties together with improved drape and soft touch properties. On the other hand, they possess disadvantages that they lack mechanical strength and dimensional stability due to the absence of firm fiber bonding.
Furthermore, they also possess another disadvantage that their mechanical strengths in the longitudinal and transverse directions are not balanced because continuous lines are formed in the web in the machine direction by the jet streams of high pressure fluid in the manufacturing process. The imbalance of this kind in mechanical strength may be avoided by applying cross-layer process. However, the crossing-over the web and/or laminating process unfavorably brings about the thickening of resultant nonwoven fabrics and adversely affects the productivity.
In order to solve these problems, various methods have been proposed. Japanese Patent Laid-Open Publication No. 54-82481 discloses a use of nonwoven fabrics made of staple fibers as a reinforcing base material. Japanese Patent Laid-Open Publication No. 54-101981 and No. 61-225361 disclose the use of woven or knitted fabric or nonwoven fabric as a reinforcing material. Japanese Patent Laid-Open Publication No. 59-94659 discloses the use of wood pulp as a reinforcing base material. Japanese Patent Laid-Open Publication No. 01-321960 and No. 04-263660 disclose a process of entangling card web with a reticular base material. Japanese Patent Laid-Open Publication No. 04-333652 and No. 04-153351 disclose a process of entangling card web with spun-bonded nonwoven fabric.
With these prior art techniques, although it is possible to improve the mechanical strength of hydroentangled nonwoven fabrics made, it is not possible to produce, in an economical and simple manner, a thin, lightweight nonwoven fabric having improved balance in strength while retaining its properties such as softness, lint-freeness, drape property and soft touch feeling which are the characteristics of hydroentangled nonwoven fabric.
The incorporation of a cross-layer process in order to improve the balance in mechanical strength of a nonwoven fabric usually brings about the lowering of productivity in the web formation process to a level of 1/2 to 1/5. In addition, the productivity of subsequent hydroentangling process is also lowered. Even when similar process is done during hydroentangling process or in the subsequent process, similarly, it is not possible to avoid the reduction of productivity. As described above, however, it is apparent that there has not been established any suitable technology to produce a hydroentangled nonwoven fabric having improved properties together with balanced longitudinal and transverse strengths without sacrificing the inherent high productivity of the web formation and hydroentangling processes.